Spatiotemporal diversity of Atlantic Niño and associated rainfall variability over West Africa and South America

A phenomenon known as Atlantic Niño is characterized by the appearance of warm sea surface temperature anomalies (SSTAs) in the eastern equatorial Atlantic in northern summer. When it attains its full strength, it increases rainfall and the frequency of extreme flooding over the West African countries bordering the Gulf of Guinea and in northeastern South America. Atlantic Niño thus has a direct socioeconomic impact in emerging countries in these regions. However, not all Atlantic Niño events are alike. Some appear earlier than others or persists longer. These variabilities during the onset and dissipation phases are well captured by the four most recurring Atlantic Niño varieties identified in a study recently published in Geophysical Research Letters (Valles-Casanova et al., 2020). Largely consistent with the differences in the timings of onset and dissipation, these four varieties display remarkable differences in rainfall response over West Africa and South America. Most of the varieties are subject to preconditioning in northern spring by cold SSTAs in the North Atlantic or El Niño in the Pacific, except for one variety with no clear source of external forcing.

Adapted from Figure 2 of Valles-Casanova et al., (2020): Time‐longitude plots of the tropical Atlantic SSTAs (averaged over 3°S–3°N; shades) illustrate the four most frequently recurring Atlantic Niño varieties during 1948–2019, namely, (a) the early‐terminating, (b) persistent, (c) early‐onset, and (d) late‐onset varieties. Land precipitation anomalies over South America (averaged over 0°–10°N and 70°W–50°W; orange lines) and West African sub‐Sahel region (averaged over 0°–10°N and 20°W–20°E; green lines) are also shown for each of the four Atlantic Niño varieties. The units for SST and precipitation are in °C and mm days^-1, respectively.

Vallès‐Casanova, I., Lee, S.‐K., Foltz, G. R., & Pelegrí, J. L. ( 2020). On the spatiotemporal diversity of Atlantic Niño and associated rainfall variability over West Africa and South America. Geophysical Research Letters, 47, e2020GL087108.  https://doi.org/10.1029/2020GL087108